1. Field of the Invention
The present invention relates to an engine operated working machine covered by a soundproof case entirely, particularly to such a machine constructed to reduce exhaust sound level and flow velocity of exhaust discharged outside of the soundproof case.
2. Discussion of Relevant Art
Engine operated working machine having an engine combined integrally with a generator, an air compressor or a water lifting pump are known, and are used at on a construction work site, generally. Many of the engine operated working machines are covered by soundproof cases entirely in order to reduce operation noise at a lowest level possible, in view of working environment or taking influences on a local society into consideration in case of operating the machines in a town especially at night.
This kind of engine operated working machine is made so that the number of openings such as a suction port and an exhaust port is fewest possible and the sizes of the openings are small in order to attain quiet operation. Therefore, on the one hand, some sufficient measures become necessary with regard to poor cooling ability within the soundproof case caused by the small area of the openings.
Regarding such a problem, an engine operated working machine as shown in Japanese Utility Model Publication No. Sho 64-3777 has been proposed. In this machine, an engine and a muffler are covered by a duct to be isolated from other instruments within the soundproof case and cooling air is forced into the duct to be discharged from the muffler side of the duct toward the outside of the soundproof case, so that re-circulation of hot exhaust cooling air into the soundproof case can be prevented and the instruments can be arranged utilizing the space within the soundproof case effectively.
In the above proposed machine, an exhaust port for discharging the exhaust cooling air from the soundproof case is disposed on an extended line of an exhaust pipe as shown in FIG. 4 of the Japanese Publication. Therefore, the exhaust cooling air is discharged forcibly by an exhaust gas from the muffler, but directness of the exhaust gas and the exhaust cooling air at the exhaust port is intense and sometimes a large exhaust sound is felt.